We have made major progress in all of the original specific aims of our investigations of the factors that regulate a murine autoimmune disease during the last grant support period. Our analysis of the relationship between expression of an autoreactive T cell receptor and virally-induced autoimmune disease indicated an important role for central tolerance (negative selection). However, the relative impact of central and self-tolerance mechanisms in disease prevention could not be directly assessed. We are now in a good position to define the relative contributions of central and peripheral tolerance mechanisms to the generation and maintenance of self-tolerance in the experimental plan that we propose for the next period of requested grant support. First, we will continue to delineate the molecular basis of aTCR-coupled signaling pathway that culminates in thymocyte negative selection (SA1) and use this information to test the effects of defective central tolerance on the development of autoimmune disease (SA2). In SA3, we will establish the impact of peripheral regulation on self-tolerance, using mice deficient in either regulatory CD4+ or CD8+ T cells. These studies will allow a clear separation of the contribution of peripheral T cell regulation from central (deletional) tolerance mechanisms. Our progress over the past grant period has provided us with the experimental and conceptual foundations that will allow us to define the relative impact of central and peripheral mechanisms in maintenance of self-tolerance and prevention of autoimmunity after either viral infection or deliberate exposureto self-antigens in the context of heightened innate immune responses.